Field of the Invention and Related Art
The present invention relates to a thin-film resistor element in which a protective film (layer) made of an electrical insulator is disposed on a heating resistor, an ink jet head employing such a thin-film resistor element, and an ink jet recording apparatus in which such an ink jet head is mounted.
Thin-film resistor elements are used in, for example, a thermal head used for thermal printing on sheets of heat sensitive paper and an ink jet recording head used in the ink jet recording process in which ink is heated and discharged in bubbles.
The above-described thin-film resistor element always has a heating resistor for generating heat. In addition to the heating resistor, most thin-film resistor elements have a protective film on the heating resistor for various reasons, such as to prevent oxidation of the heating resistor or improve the wear resistance of the heating resistor.
The ink jet recording process assures high-speed, high-density and high-definition recording exhibiting a high image quality and is suited for color and compact recording. Thus, the ink jet recording process has been drawing attention in recent years. The thin-film resistor element for an ink jet recording head, however, requires a protective film which performs better than that for a thermal head, because the heat acting portion of the ink jet recording head makes direct contact with the ink, because the heat acting portion is subjected to a large mechanical shock due to cavitation which occurs when ink bubbling and bursting is repeated, and because changes in temperature of several hundred degrees occur in the heat acting portion in an extremely short period of time, e.g., in the order of 10.sup.-1 to 10 microseconds. Generally, recent technologies allow the formation of an electrical insulating layer made of, for example, SiO.sub.2, SiC or Si.sub.3 N.sub.4, on the heating resistor as the protective film for the ink jet head, or the formation of both such an electrical insulating layer on the heating resistor and a cavitation resistant layer made of, for example, Ta on the electrical insulating layer, as the protective film.
In a thin-film resistor element with any of the above-described protective films provided therein, the protection capability and stability of the protective film dominate the durability of the element. Thus, the formation of a protective film exhibiting the highest possible reliability has been of a great technical interest.
However, the above-described thin-film resistor element has a problem in that a particular film forming process used to form a protective film on the heating resistor in the manufacture of the thin-film resistor elements produces many defective thin-film resistor elements by which the protective film readily swells or peels off when the heating resistor is energized, particularly when the heating resistor is repetitively energized, even if the same material or the same structure is employed to form the protective film. In such a thin-film resistor element in which the above-described defect has occurred, the resistor may break because it is no longer in thermal contact with the protective film. In the ink jet head, the generation of the defect reduces thermal conductivity of the ink and the ink may not be discharged.